1. Field of the Invention
This invention relates to a method and apparatus for effecting the gravel packing of a plurality of spaced production zones provided in a subterranean well by a single trip of a work string incorporating the gravel packing apparatus into the well.
2. Description of the Prior Art
Of considerable magnitude in the production of hydrocarbons, such as oil and gas, from a producing well is the problem of sand flow into the well bore from unconsolidated formations. Production of sand with the flow of hydrocarbons will cause the well bore to gradually fill up with minute sand particles until production perforations in the casing and, oftentimes, the end of production tubing inserted therein, are covered, resulting in a significant reduction in fluid production. In many instances, sand production will cause the well to stop producing.
In addition to reduction of fluid production, flow of sand also may cause severe damage to equipment, such as pumps, chokes and the like. In flowing wells, fluid velocity may be sufficient to scavenge sand within the well bore and produce it with the fluid hydrocarbon, resulting in holes being cut in the tubing and flow lines.
One well known means of controlling flow of sand into the well bore is the placement of gravel on the exterior of a slotted, perforated, or other similarly formed liner or screen (hereafter referred to as "production screen") to filter out sand produced with the oil or gas, and thus prevent its entry into the well bore. It is important to size the gravel for proper containment of the sand. Additionally, the slotted liner or screen must be designed to prevent entry of the gravel itself into the production tubing.
Although other fluids have been used, treated and filtered production or nearby well or surface water, to which is generally added a desired concentration of calcium chloride or other active substance, is preferably used in most gravel packing processes during the cleaning or flushing procedure. The water is treated to remove contaminates such as cement particules, scale, and other foreign material generally resulting from the circulation of the water in the well bore.
Apparatus for gravel packing production zones of wells are well known, and a variety of apparatus is commercially available for effecting such operation. See for example, U.S. Pat. Nos. 3,901,318, 3,913,676 and 4,044,832.
All of such prior art devices have, however, required multiple trips of the work string incorporating the gravel packing apparatus into the well in order to effect the gravel packing of a plurality of production zones.
It would be economically desirable where multiple production zones are to be gravel packed in a subterranean well, that the required multiple gravel packing operations should be capable of being accomplished in a single trip of the work string into the production zone of the well. The present invention affords such means and method.